Widespread bar code technologies such as the universal product code (UPC) and others rely upon predefined symbol sets defined for certain positions and sizes within labels and other media. The traditional UPC, such as that illustrated in FIG. 1, and related codes however do not achieve a particularly high information density in terms of bits embedded per square inch, achieving on the order of 100-300 bits per square inch. This is due in one regard to the length and width of the code dimensions, which are comparatively elongated. This is also due in another regard to the limitation of the encoding technology to a black and white color scheme, in which the presence or absence of bits is represented by a black or white mark or symbol. While this encoding scheme may enhance detection robustness because the separation between coding symbols in terms of color space distance is greatest, and permit the use of relatively low-cost scanners because only black and white elements need to be discriminated, a price is paid in terms of information density. Simple black and white bar codes have therefore as a rule proved insufficient or impractical for transaction or identification applications which demand greater overall information content, such as driver's licenses or other ID media.
As the pixel resolution of both printing devices such as laser printers and detection devices such as handheld scanners has increased, the possibility has correspondingly arisen to enlarge the color space in which bar codes and other symbol codes may be expressed. Printing devices, and scanning or input devices in particular have become available which are capable of close-contact optical or other scans at color depth resolutions of 8 bits (256 grayscale or color), 24, 32, 48 or greater bit depths. Enlarged color spaces combined with finer spatial resolution creates the potential for greater information density on media, yet encoding, for example, a driver's license at 32 bits per pixel at 200 lines per inch may cause scanning errors from discolored paper, pixelation, misalignment and other problems, so that while information density may increase, accuracy may in cases be compromised. Other problems in bar code and related encoding technology exist.